The present invention generally relates to measuring the temperature of a surface of a rail utilizing sensor or sensors embedded underneath of a stationary or moving rail car. The techniques utilized in this invention are useful in estimating the rail surface temperature to aid the locomotive engineer to make appropriate decisions taking into account rail surface temperatures prevailing at any given time and location.
There is great interest in monitoring rail surface temperatures primarily as a mechanism to assure the safety of the railroads. In this discussion “rail temperature” is used to denote the temperature of a surface of a segment of a rail. Most fundamentally, monitoring rail surface temperatures would allow a locomotive engineer to detect an unusually high rail temperature and take necessary action, such as reducing speed. Track engineers have long recognized the benefits of being able to measure rail neutral temperature (RNT) of a rail easily and non-destructively. The RNT is the temperature at which the rail has no longitudinal thermal force. Compressive forces are produced when the rail temperature is higher than the RNT and the rail is in tension at temperatures below the RNT. Excessive tensile forces can cause rail joints to fail or pull apart in cold weather and high compressive forces affect lateral stability of a track and can cause the track to buckle. It is common practice for railroads to issue territory-specific slow-down orders in days with high ambient temperatures. On a sunny day, rail temperatures can exceed the ambient temperature by as much as 40° C. Therefore the rail temperatures can vary between −40° C. and 80° C. throughout the year. Numerous factors affect track buckling. Among them, an important factor is instantaneous rail temperature. Unfortunately, is not is easily obtainable when the rail is moving. Thus there is a great need to obtain instantaneous rail temperature. Measured rail temperatures may also find use in validating rail temperature prediction models.
Rail temperatures are currently being measured using surface thermometers. However, these instruments yield single point measurements, thereby requiring a prohibitively high number of them for monitoring any long section of a rail, which in turn, can be cost-prohibitive. Multiple wavelength infrared intensity measurements constitute a dominant temperature sensing technology in a wide variety of applications. Currently, there are several commercial multi-wavelength infrared pyrometers that provide temperature of objects with a high degree of accuracy. However, the lack of temporal and spatial resolution precludes their direct use in estimating rail temperatures from a moving rail vehicle. Commercial non-contact temperature measurement sensors are currently available. However, these sensors use a single-wave length in the far infrared spectral region. In this portion of the infrared spectrum, dynamic range is limited, especially at lower temperatures. Even high rail temperatures of the order of 65 C are considered low temperatures for these sensors. For many commercial non-contact sensors, an emissivity value is given for a surface of the rail and the emissivity is assumed to be constant. If the emissivity value of the rail deviates the rail surface deviates from this fixed value, the temperature output by the sensor will be inaccurate. Thus it is important that the temperature output by a sensor be independent of the emissivity of the surface of the rail. Thus a need exists to monitor the rail temperature along long sections of the rail even as the rail car is moving, providing accurate rail temperature information to the locomotive engineer, without fixing a constant value for the emissivity of the surface of the rail.